This
appears to be the first evidence that visual cues can affect the rate of sexual
maturation of a species.

"This
effect shouldn't be limited to just this one species we studied here,"
evolutionary ecologist Craig Walling at the University of Exeter told LiveScience.

Walling
and his colleagues investigated green swordtail fish, a Central American species
popular in the tropical aquarium market. The fish is named after the striking
green sword-like ornament males have extending from their tailfins, making themappear
larger and more attractive to females.

"They're
a very visually oriented species," Walling explained.

The
researchers kept juvenile and adult green swordtails in separate tanks so they
could see each other through the glass but not use their other senses. Walling
and his colleagues discovered young females shown males with long swords
reached sexual maturity up to four months faster than females who weren't. At
the same time, young males shown adults with impressive swords matured later
than others that were shown less attractive adults.

The
researchers speculated this effect helps females maximize
their chances for quality mates and helps males avoid competition from more
attractive males. "You would suspect that physical things like nutrition
would have an effect on sexual maturation, so it's very surprising that just
visual cues do," Walling said.

Regarding
whether or not similar effects might be seen in humans, "humans are
becoming sexually mature at earlier ages, but that's most likely due to
improvements in nutrition and health, and not to watching too many Johnny Depp
or Brad Pitt films," Walling said.

Still,
this effect might be seen in other species and could affect conservation of
endangered animals, Walling said. "In order to conserve something, it has
to be sexually mature, so it's important to understand what contributes to its
maturation," he said

Future
research could also see whether other visual cues affect sexual maturation,
such as the presence of predators.

Walling
and his colleagues report their findings this Valentine's Day in the journal Biology
Letters.